Electrographic carrier vehicle and developer composition

ABSTRACT

AN ELECTROGRAPHIC CARRIER VEHICLE AND DEVELOPER COMPOSITION CONTAINING SAID CARRIER VEHICLE ARE DESCRIBED. THE CARRIER VEHICLE IS COMPOSED OF MAGNETICALLY-ATTRACTABLE CORE PARTICLES HAVING A RESINOUS VINYLIDENE CHLORIDE-CONTAINING COPOLYMER COATING THEREON.

United States l atent O U.S. Cl. 252-62.1 8 Claims ABSTRACT OF THE DISCLOSURE An electrographic carrier vehicle and developer composition containing said carrier vehicle are described. The carrier vehicle is composed of magnetically-attractable core particles having a resinous vinylidene chloride-containing copolymer coating thereon.

This invention relates to electrography and to a magnetically responsive particulate carrier vehicle and a dry electrographic developer composition containing such a carrier vehicle useful, for example, in the magnetic brush development of latent electrostatic charge images.

Electrographic imaging and developing processes, e.g. electrophotographic imaging processes and techniques, have been extensively described in both the patent and other literature, for example, U.S. Pat. Nos. 2,221,776, Carlson, issued Nov. 19, 1940; 2,277,013, Carlson, issued Mar. 17, 1942; 2,297,691; Carlson, issued Oct. 6, 1942; 2,357,809, Carlson, issued Sept. 12, 1944; 2,551,582, Carlson, issued May 8, 1951; 2,825,814, Walkup, issued Mar. 4, 1958; 2,833,648, Walkup, issued May 6, 1958; 3,220,- 324, Snelling, issued Nov. 30, 1965; 3,220,831, McFarlane, issued Nov. 30, 1965; 3,220,833, McFarlane, issued Nov. 30, 1965, and many others. Generally these'processes have in common the steps of forming a latent electrostatic charge image on an insulating electrographic element. The electrostatic latent image is then rendered visible by a development step in which the charged surface of the electrographic element is brought into contact with suitable developer mix.

One method for applying the developermix is by the well-known magnetic-brush process. Such a process generally utilizes apparatus of the type described, for example, in U.S. Pat. No. 3,003,462, Streich, issued Oct. 10,

1961, and customarily comprises a non-magnetic rotatably mounted cylinder having fixed magnetic means mounted inside. The cylinder is arranged to rotate so that part of the surface is immersed in or otherwise contacted with a supply of developer mix. The granular mass comprising the developer mix is magnetically attracted to the surface of the cylinder. As the developer mix comes within-the influence of the field generated by the magneto means within the cylinder, the particles thereof arrangethemselves in bristle-like formations resembling a brush. The bristle formations that are formed by the developer mix tend to conform to the lines of magnetic flux, standing erect in the vicinity of the poles and laying substantially flat when said mix is outside the environment of the magnetic poles. Within one revolution the continually rotating cylinder picks up developer mix from a supply source and returns part or all of this material to the supply. This mode of operation assures that fresh mix is always available to the surface of the photoconductive element at its point of contact with the brush. In atypical rotational cycle, the roller performs the successive steps of developer mix pickup, brush formation, brush contact with the electrographic element, e.g. a photoconductive element, brush collapse and finally mix release. i

In magnetic-brush development of electrostatic images the developer is commonly a triboelectric mixture of fine 3,795,617 Patented Mar. 5, 1974 ice toner powder comprised, for example, of a dyed or pigmented thermoplastic resin with coarser carrier particles of 'a magnetic material such as iron particles, etc.

The relatively high conductivity of uncoated iron and similar ferromagnetic carrier particles can be useful in magnetic-brush development because a conducting magnetic brush serves effectively as a development electrode, and as a consequence, the fringing field created in an electrostatic latent image is modified and solid area development is achieved. However, in many cases, solid area development by such a means has a disadvantage of very narrow exposure latitude. Accordingly, there is a need for a magnetic-brush development composition which is capable of producing acceptable solid area images within a wide range of exposure latitude.

Resinous coatings on iron or other magnetic-brush carrier granules can aid in increasing the surface resistance and the tendency towards fringing development. However, application of a suitable insulating resin may pose a number of other problems. For example, it may be difficult to obtain a uniformly coated magnetic carrier particle having a resinous coating of sufiicient minimum thickness to greatly increase the electrically resistance of the carrier particle without substantially reducing the bulk density of the magnetic particles. One way to overcome this problem is described in Miller, copending application Ser. No. 119,061, filed Feb. 25, 1971, and now abandoned, which describes a developer composition containing magnetic carrier particles having two or more coatings of a resinous material applied thereon such that there is no substantial dissolution of one resinous layer into an adjacent resin layer. Another problem associated with magnetic carrier particles is the amount of background scum which may be deposited on a surface of a reuseable photoconductive element contacted by the magnetic carrier particles. Thus, if one desires to utilize resin-coated magnetic carrier particles, it is advantageous to utilize resin coatings on such carrier particles which minimize the amount of background scum which may be deposited on reusable photoconductive elements. Certain carboxylated resin coatings such as described in Miller, U.S. 3,547,822, issued Dec. 15, 1970, have been found to aid in reducing scrum deposits.

Additionally, when using resin-overcoated magnetic carrier particles, it is advantageous to provide a resin overcoat on the magnetic carrier particle such that when the overcoated carrier particles are utilized with an electroscopic toner powder, there is produced a high net electrical charge on the toner powder due to the electrical interaction between the toner powder and resin coated carrier particles. The reason for employing a carrier particle which, when utilized with electroscopic toner powders, produces a high net toner charge is to aid in reducing the amount of toner throw-01f, i.e., the amount of toner thrown out of the developer mix as it is agitated in the magnetic brush development apparatus.

Advantageously, the resin overcoat selected should comprise an overcoat material which can be readily applied to the carrier particle and which exhibits good adhesion to the carrier particle without requiring the use of special binding agents. It is also important to utilize as a resin coating, a resin which is not easily worn off the carrier particle. That is, the resin coating should exhibit good resistance to abrasion.

In addition to the literature noted above which describes particular types of coatings on magnetic carrier particles, var'ous other resinous coatings which may be applied to carrier particles are decribed, for example, in U.S. Pats. 2,618,551 issued Nov. 18, 1962; 2,818,552 issued Nov. 18, 1952; 2,874,063 issued Feb. 17, 1959 and 3,526,533 issued Sept. 1, 1970. As is apparent, from the work described, for example, in the foregoing publications, a large number of resinous coating materials have been suggested for use in coating magnetic carrier particles. It is equally apparent, in view of the above discussion, that a major problem facing the art has been to discover particular individual resin(s) which, when coated on carrier particles used in developer mixes, enable one to solve or substantially reduce each of the above-noted problems.

In accordance with the present invention it has been discovered that magnetically-attractable core particles having on the outer surface thereof a resinous coating comprising certain copolymeric materials as defined hereinafter provide an effective particulate carrier vehicle for an electrogr-aphic developer.

The copolymeric materials useful in the invention are copolymerized blends of vinylidene chloride; at least one member of the group acrylonitrile, methacrylonitrile, and an alkyl ester of an acrylic or methacrylic acids having from 1-18 carbon atoms in the alkyl group; and at least one acidic organic compound containing 3 to about 12 carbon atoms, at least one polymerizable vinylidene moiety and at least one carboxylic acid (-COOH) or sulfonic acid (SO H) moiety.

According to a preferred embodiment of the invention, the copolymeric material is a vinylidene chloride-acrylonitrile-acrylic acid terpolymer containing from about 5 to about 30% by weight of acrylonitrile, from about 2 to about 25% by weight of acrylic acid, and from about 55 to about 93% by weight vinylidene chloride. 'In accordance with the invention, it has been found that such a carrier vehicle in admixture with a suitable electroscopic toner powder imparts a relatively high net toner charge to the toner powder particles and thereby substantially reduces the amount of toner throw-01f. In addition, electrographic-developers containing such terpolymeric coated carrier particles substantially reduce the amount of background scum deposited on a reusable photoconductive surface and are capable of producing continuous-tone solid area images as well as fine-line images. Moreover, such terpolymeric coatings may be applied directly to the magnetically attractable core par ticles without the use of separate bonding agents; and, when so applied, exhibit a high degree of abrasion resistance.

Although copolymeric materials useful in the present invention may be used which have a composition outside the specific compositional ranges described immediately above, it has been found that copolymeric materials having an organic acid content substantially higher than 25% by weight tend to exhibit decreased environmental stability at high relative humidity.

The core materials which can suitably be coated to form carrier particles in accordance with this invention include a variety of magnetic materials. The phrase magnetic materials as used herein encompasses a variety of magnetically attractable materials. Particularly useful materials would include ferromagnetic materials such as the metals of the first transition series, i.e., nickel, iron, cobalt, and alloys and mixtures thereof. Other useful materials which exhibit a net magnetic moment are the ferrimagnetic materials. Examples of such ferrimagnetic materials would include the ferrites, which are materials having the general formula MeO-Fe O where Me is a metal ion, as well as mixed ferrites, which contain more than one species of metal ion in addition to iron, and the substituted ferrites, in which another metal replaces some of the iron. Also included in the phrase magnetic material are particles such as those described in Miller, Canadian 835,317 issued Feb. 24, 1970, and which are comprised of, for example iron dispersed in a resin binder. Such magnetic materials are used as a core in accordance with this invention over which is coated the above-described copolymeric resin. The core can consist of a solid particle of magnetic material or can be a nonmagnetic particle overcoated with ferromagnetic materials as described in Belgian Pat. No. 726,806, dated Mar.v 14, 1969. The core can comprise rough-surfaced magnetically responsive particles; smooth-surfaced magnetically responsive particles; or a mixture of rough-surfaced and smooth-surfaced magnetically responsive particles. Particles having these varying surface properties and mixtures thereof are more fully described in Trachtenberg et al., copending patent application U.S. Ser. No. 236,724 filed concurrently herewith and entitled Electrographic Carrier Vehicle and Developer CompositionCase A.

A magnetic core can vary in size and shape with core particles having an average diameter of from about 1200 to about 30 microns. Particlarly useful results are obtained with core materials of from about 300 to about 60 microns average diameter. The size of the core particles used will, of course, depend upon several factors such as the type of images ultimately developed, desired thickness of the polymeric resin coating, etc. The phrase average diameter as used herein is not meant to imply that only perfectly uniformally dimensioned particles can be used. This phrase is used to refer to the average thickness of particles when measured along several axes. Average diameter also refers to the approximate size of the openings in a standard sieve series which would just retain or just pass a given particle. In addition, it may be noted that the core materials useful in the -present invention may be subjected to various treatments to modify their surface properties prior to being coated with the above-described terpolymer. For example, it may be desirable to wash the magnetic core in an acid-wash, rinse and subject the washed particles to controlled drying conditions so as to induce or exclude oxidation of the surface of the carrier particles. Such treatments are especially useful when the magnetic core comprises iron particles. Such treatment processes are described more fully in Belgian Pat. 746,109 dated Apr. 30, 1970.

In accordance with this invention, the magnetic core particles are coated by a liquid resin application of the above-described copolymer to form a resultant resinous coating which, when dried, forms a thin highly adherent coating all or only certain portions of the outer surface of the magnetic core particles. Typically, sponge iron core carrier particles have a resin coating varying from about 0.01 to about 0.6 microns in thickness, preferably from about 0.01 to about 0.3 microns in thickness. No special binding agent compositions are necessary to adhere the resin coating to the magnetic core particle thus providing one of the advantages of the resin coatings useful in the present invention. Typically, the resultant coated carrier particle bears a copolymeric coating which comprises about 0.001 weight percent to about 3 weight percent of the total weight of the coated carrier particle. (The aforementioned weight percents are based on the resultant carrier particlebearing a dry resin overcoat.) The coatings may be applied to the core material by a variety of well known techniques including spraying a liquid mixture containing the copolymer on the magnetic core, applying the resin by a fluidized bed coating technique, dipping the magnetic core particles into a trough filled with a liquid mixture containing the above-described copolymer, etc. The liquid application of the above-described copolymers may be from either a dispersion or solvent solution of the copolymer material. The copolymer materials useful in the invention may be conveniently dissolved or dispersed in organic solvents or dispersed in water. Following the application of the liquid-form copolymer to the magnetic core, the liquid vehicle is evaporated and the resin is allowed to dry and harden. It may also be possible to coat from a liquid melt of the co polymer providing the amount of the resin used is kept low enough. In general, the concentration of resin in the liquid coating vehicle is usually quite low to insure that the particles do not become agglomerated during coating.

As noted, according to a preferred embodiment of the invention, the copolymeric materials useful in the invention are vinylidene chloride-acrylonitrile-acrylic acid terpolymers. However, useful results are also believed possible by substituting one or more alkyl esters of acrylic or methacrylic acid for the acrylonitrile component of the copolymer. Typically, such esters have from 1-l8 carbon atoms in the alkyl group and include, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, n-dodecyl methacrylate, n-octadecy methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc. Similarly, useful results are believed attainable wherein methacrylonitrile is substistuted for the acrylonitrile component.

Typical, the acid content of the copolymeric materials useful in the invention is less than 2 milliequivalents of 1 N.NaOH per gram of polymer based on the dry weight of said polymer. In the preferred embodiment of the invention using a terpolymeric coating of vinylidene chlorideacrylonitrile-acrylic acid, the acid content is within the range of from about 0.3 to about 1.0 milliequivalents of l N.NaOH per gram of polymer based on the dry weight of the polymer. A typical copolymeric material useful in the present invention has a molecular weight roughly on the order of about 200,000. Copolymeric materials having molecular weights substantially lower or substantially higher than 200,000 may also be used.

As indicated, it is believed that various acidic organic compounds may be substituted for the acrylic acid monomer used in the preferred terpolymeric coating of applicants invention. Typically, such acidic compounds should contain from 2 to about 12 carbon atoms, at least one polymerizaible vinylidene group, and at least one carboxylic or sulfonic acid moiety. Typical of such acids are itaconic acid, methacrylic acid, vinyl benzoic acid, sulfoalkyl methacrylates and sulfoalkylacrylates such as sulfoethylmethacrylate, etc. Sulfoethylmethacrylate may be represented by the following structural formula:

There are various known ways of making the aforedescribed copolymeric materials. The monomers may be copolymerized by any known method to form the copolymers used in accordance with this invention. For example, the copolymerization may be conducted in aqueous emulsion containing a mixture of the monomers, a catalyst and activator, e.g. ammonium persulfate and meta sodium bisulfite, and an emulsifying and/or dispersing agent. Alternatively the copolymers of this invention may be prepared by polymerization of the monomeric components in bulk without added diluent, or the monomers may be reacted in appropriate organic solvent reaction media. The total catalyst-activator concentration may generally be kept within a range of about 0.01% to about 2.0 by weight of the monomer charge, and preferably within a range of concentration of 0.1% to 1.0%. Improved solubility and viscosity values are obtained by conducting the polymerization in the presence of mercaptans such as ethyl mercaptan, lauryl mercaptan, tertiary dodecyl mercaptan, etc., which are cfiective in reducing crosslinking in the copolymer. In general, the mercaptans should be used in concentrations of 0.1% to 5.0% by weight based on the weight of polymerizable monomers present in the charge.

In general, the electrical resistivity of the copolymer coated carrier particles of the present invention may be characterized as having intermediate or high electrical resistivities. Typically these coated particles have resistivities greater than about ohms to 10 ohms and higher up to and above 10 ohms. The intermediate resistance carrier particles of this invention generally have an electrical resistance within the range of from about 10 ohms to about 10 ohms. Generally, using carrier particles having a resistivity within this intermediate range, there is obtained a form of development varying from semi-solid to semi-fringing development of images having uniform solid areas. At the low and at the high ends of this range of resistivities, i.e. 10 ohms and 10 ohms, respectively, development very closely approximates true solid area and true fringing development, respectively. For purposes of comparison, the resistance of the various carrier particles of the invention is measured in a standard magnetic brush resistance test. This test is conducted each time using a 15 gram quantity of carrier particles. A cylindrically shaped bar magnet having a circular end of about 6.25 square centimeters in area is used to attract the carrier and hold it in the form of a brush. After formation of the brush, the bar magnet is then positioned with the brush-carrying end approximately parallel to and about 0.5 centimeters from a burnished copper plate. The resistance of the particles in the magnetic brush is then measured between the magnet and the copper plate, using a General Radio D.C. Electrometer (Type 1230-A, 6-9 volts).

Electrostatic developer compositions of the present invention can be prepared by mixing from about to about 99% by weight of the above-described carrier vehicle with from about 10 to about 1% by weight of a suitable electroscopic toner material.

The toner material (or marking particles) useful in dry electrographic developer compositions of the present invention are generally comprised of a resin binder in a colorant. Suitable toners can be selected from a wide variety of materials to give desired physical properties to the developed image and the proper triboelectric relationship to match the carrier particles used. Generally, any of the toner powders known in the art are suitable for mixing in the developer composition of this invention. In certain instances, the toner may be comprised solely of colorant material without any resinous binder. In other cases, where a visible image is not desired or needed, the toner may be composed solely of a colorless material, such as a resinous material having the desired physical and triboelectric properties.

When the toner powder selected is utilized with magnetic carrier particles in a magnetic-brush development arrangement, the toner clings to the carrier by triboelectric attraction. The carrier particles acquire a charge of one polarity and the toner acquires a charge of the opposite polarity. Thus, if the carrier is mixed with a resin toner which is higher in the triboelectric series, the toner normally acquires a positive charge and the carrier a negative charge.

Useful toner particles can be prepared by various methods. Two convenient techniques for preparing these toners are spray-drying or melt-blending followed by grinding. Spray-drying involves dissolving the resin, colorant and any additives in a volatile organic solvent such as dichloromethane. This solution is then sprayed through an atomizing nozzle using a substantially non-reactive gas such as nitrogen as the atomixing agent. During atomization, the volatile solvent evaporates from the airborne droplets, producing toner particles of the uniformly colored resin- The ultimate particle size is determined by varying the size of the atomizing nozzle and the pressure of the gaseous atomizing agent. Further details relating to spray-drying may be found in Carlson, US. Pat. 2,357,809 issued Sept. 12, 1944, and in West, US. Pat. 3,166,510 issued Jan. 19, 1965. conventionally, particles of a diameter between about /zp. and about 30p are used, with particles between about 2n and 15a being preferred, although larger or smaller particles can be used where desired for particular development or image considera tions.

Suitable toners can also be prepared by melt-blending.

This technique involves melting a powdered form of polymer or resin and mixing it with suitable colorants and additives. The resin can readily be melted or heated on compounding rolls which are also useful to mix or otherwise blend the resin and addenda so as to promote the complete intermixing of these various ingredients. After thorough blending, the mixture is cooled and solidified. The resultant solid mass is then broken into small pieces and finely ground to form a free-flowing powder of toner particles. Such a melt-blending technique is described in Walkup, U.S. Pat. 2,618,551 issued Nov. 18, 1951. Of course, various other techniques for making toner particles may also be used. For example, certain spray-freeze drying techniques may be modified to provide useful methods for preparing toner particles. An example of such a modified spray freeze drying technique is described in Product Licensing Index, volume 84, April 1971. The resultant toner particles usually range in size from about /2 to about 30 The resin material used in preparing the toner can be selected from a wide variety of materials, including natural resins, modified natural resins and synthetic resins. Exemplary of useful natural resins are balsam resins, colophony,.and shellac. Exemplary of suitable modified natural resins are colophony-modified phenol resins and other resins listed below with a large proportion of colophony. Suitable synthetic resins are all synthetic resins known to be useful for toner purposes, for example, polymers, such as certain polycarbonate resins described in US. patent application Ser. No. 34,557 filed May 4, 1970 and now US. Pat. No. 3,694,359, and in Product Licensing Index, volume 84, April 1971, vinyl polymers and copolymers including polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl ether, polyacrylic and polymethacrylic esters, polystyrene, including substituted polystyrene; polycondensates, e.g., polyesters, such as phthalate, terephthalic and isophthalic polyesters, maleinate resins and colophonymixed esters of higher alcohols; phenolformaldehyde resins, including modified phenol-formaldehyde condensates; aldehyde resins; ketone resins; polyamides; polyurethanes, etc. Moreover, chlorinated rubber and polyolefins, such as various polyethylenes, polypropylenes, polyisobutylenes, are also suitable. Typical toner materials having incorporated therein styrene containing materials are disclosed in the following U.S. Pats: 2,917,460, Solar, issued Dec. 15, 1959; Re. 25,136, Carlson, issued Mar. 13, 1962; 2,788,288, Rheinfrank et al., issued Apr. 9, 1957; 2,638,416, Walkup et al., issued Apr. 12, 1953; 2,618,552, Wise, issued Nov. 18, 1952; and 2,659,670, Copley, issued Nov. 17, 1953. Other useful styrene containing toner resins are copolymers prepared from a monomeric blend of (a) 40-60% by weight styrene or styrene homolog; (b) 2050% by weight of lower alkyl acrylate and methacrylate, e.g. alkyl methacrylates and alkyl acrylates having up to 3 carbon atoms in the alkyl group; and (c) 530% by weight of higher alkyl acrylates and methacrylates, e.g. alkyl methacrylates and alkyl acrylates having 620 or more carbon atoms in the alkyl group.

Colorants useful in the practice of this invention can be selected from a variety of materials such as dyestuffs or pigments. Such materials serve to color the toner and thus render it more visible. Suitable toner materials having appropriate caking and charging properties can, of course, be prepared without the use of a colorant material where it is desired to have a developed image of low optical opacity. In those instances where it is desired to have high optical opacity, the colorants used can, in principle, be selected from virtually all of the compounds mentioned in the Color Index, vols. I and 11, Second Edition. Included among the vast number of useful colorants would be such materials as Hansa Yellow G (CI. 11680), Nigrosine Spirit soluble (C.I. 50415), Chromogen Black ETOO (CI. 14645), Rhodamine B (CI. 45170), Solvent Black 3 (Cl. 26150), Fuchsine N (C.I. 42510), C. I. Basic Blue 9 (CI. 52015), etc. Another useful class of colorants is comprised of nigrosine salts such as nigrosine salts of monoand di-functional organic acids having from about 2 to about 20 carbon atoms such as chloroacetic acid, stearic acid, sebasic acid, lauric acid, azelaic acid, adipic acid, abietic acid and the like. Nigrosine salts of this type are disclosed in Belgian Pat. 734,570 dated Aug. 14, 1969. Carbon black also provides a useful colorant. The amount of colorant added may vary over a wide range, for example, from about 1 to about 20 percent of the weight of the resin binder. Particularly good results are obtained when the amount is from about 2 to about 10 percent. In certain instances, it may be desirable to omit the colorant, in which case the lower limit of concentration would be zero.

In addition, if desired, organic melt viscosity modifying agents for the resin binder may be incorporated in the toner particles. If such viscosity modifying agents are utilized, the ratio of melt viscosity modifying agent to resin binder generally can vary from about 1:3 to about 1.5 :1. Further information concerning these viscosity modifying agents may be found in Merrill et al., US. ap plication Ser. No. 23,031, filed Mar. 26, 1970 and now abandoned.

The following examples further illustrate the invention and certain advantages thereof:

Examples 1 and 2 and 5 are included for purposes of comparison. These examples are directed to developers containing various types of resin coated carrier components. Examples 3 and 4 illustrate the carrier and developer compositions of the present invention.

Each of the dry developers used in Examples 14 contains an electroscopic toner composed of particles of black pigmented polycarbonate resin as described in US. patent application Ser. No. 34,557 filed May 4, 1970 and in Product Licensing Index, volume 84, April 1971.

In these examples the term toner throw-off is defined to mean the quantity of toner powder thrown out of the developer mix of toner and carrier particles upon mechanical agitation. For purposes of comparison, a test to measure toner throw-off is devised as follows: A fixed quantity of a well-mixed developer (i.e. mixture of toner and carrier particles) is measured and placed in an open cup positioned in a device oscillating laterally through a 0.75 inch distance at 6 cycles per seconds for a fixed period of time. The toner-throw off of the developer mix due to the oscillation is collected on filter paper via a vacuum and weighed. In certain of the examples, the amount of toner throw-off is reported as milligrams of toner thrown-off (see Ex. 5). In Examples 2-4 toner throw-off is reported as Light (L), Medium (M) or Heavy (H). These designations (i.e. L, M, H) simply indicate whether there was little toner throw-off (i.e. L), large amounts of toner lost (H) or a moderate amount (M) lost. In Examples 2-4, the above-described toner throw-01f test is not used. However, roughly L would correspond to less than about 2.5 milligrams of toner, H would roughly correspond to greater than about 10 milligrams of toner throw off, and M to amounts within the range of about 2.5-10 milligrams of toner throw-01f. Combinations of markings such as H-M or L-M refer to amounts of toner throwoff at the high and low ends, respectively, of the 2.510 mg. range.

In these examples the net toner charge imparted to a toner powder is measured using a Farraday Cage in the following manner: A weighed portion of each of a developer is placed in an iron tube that is covered at one end with a 200 mesh screen that retains all carrierparticles within the tube. An air stream is then directed through the tube, blowing toner particles off the carrier, through the 200 mesh screen'at the exit and into a Farraday Cage condenser that is at an initial electrical potential of 0 volt as measured by an electrometer. As the triboelectrically charged toner particles settle on the walls of the cage, their electrical potential is measured by an electrometer. The potential obtained is converted to electrical TABLE I charge in microcoulombs and this figure is divided by the weight in grams of the toner powder particles that have Gamer figfigg settled in the Farraday Cage, thus providing the net toner Cam charge in microcoulombs per gram. The net toner charge mung is therefore the algebraic sum of the electrical charges on sr heri cal iron p as received resistivity (pcoulombs/ Image (ohms) g'.) typ s the toner particles which have settled on the walls of the o1) 3; 2 cage. 101: 5.2 8-1 The terms relating to image type are used in the accom- 38.. 3:? F panying example as follows: 0 Hal 510... 1 0 gr S means solid area development predominates. That 8 ace e u ym 1 ii 1 M is, one obtains good copies of solid area images including 5%}: good fill-in of solid area images. 100.1012 1 S 8-8 means semisolid area development predominates M h 10 0. 00 S-F c aractenzed by slight loss in density of the center of a 15 3x100 M copy of a 25 mm. square solid image. figiz g F M means medium area development predominates char- 11 1 M acterized by a large loss in density of the center of a copy M 0x10 12.3 M of a 25 mm. square solid image. 1: Q3 3 S-F means semi-fringed development predominates de M wherein little or no density is produced in the center of a nitrile (l5%)-acrylic acid (67) 10" 10.1 F-F copy of a mm. square solid image. z ggg F means fringed development predominates wherein no Saran F220 3x10 1010 M denslty 18 produced over the l t of the Internal area LEGEND.CyC101B.c 11-100 is a trademark used to identify an ABS Of a COPY Of a 25 mmsquare l d imag 25 lefiilzl rein Borg gllarneignlgrpgn M Dis a gradeimagk usedtto tildentii a diaallyl F F {means hlghlY fringed (fun filngmg dev.elopment identify polyester resin obtained from Du Pont; Durez 510 is atrademark predominates wherein the only density obtained 1n a copy useid (tfilidentiiy pllrilenoliormaldegyde leilnibtallilied froimtDueztPfl-asltics an emica s c. po ene is a re emar use 0 i en i y ow of 25 square Sohd Image Is narrow edge outline molecular weight olyethylene obtained irom Eastman Chemical Of the square. Products; Epon 828 125 is an epoxy system. The Epon 828 is a trade- EXAMPLE 1 mark used to identify the epoxy from Shell Chemical. The V125 is an amine curing agent from General Mills; Estane 5740X1 is a trademark used to identify poly-urethane elastomer obtained from B. F. Goodrich;

The fOHPWmg Table I hsts number of Carmel. surfac' Ethocel 10 is a trademark used to identify an ethyl cellulose obtained mg materials which were tried on untreated, smoothq g e 0 3 Fogn war 7/ ;0 is agragemzgk used gggde y 0 3;;

. vmy orma o aine rom onsan o 0.; anex is a re emar g i PPEg fps g z g i fi averageldlam' iged to i dseirtify a? alikyl-sigastitrditied rgilyvfinylpylrlriollidofieg irotmdGAlF;

eerwrt 1n eraneo mes 5 art 6 r anex isa ra emar use oieniyana y-susiue poyg e p 16 s a e (vinylpyrrolidone) from GAF; Ganex V904 is a trademark used to purchased from the Nuclear Metals DiVisiDn Of Whittaker identify an alkyl-subsfimted poly(vinylpyrro]jdone) from GAF; Hypa.

C0 T Ian 30 is a trademark used to identify a chloro-sulfonated polyethylene rp he polymer Sur.facmg matenals evaluated m Table from Du Pont; Kel-F 800 is a trademark used to identify a chlorotri- I are coated at 0.1 weight percent. The control toner fornuo egh n v m ndene lillaioridgresir from 31Vr 00.; k nar istaggdemaigr use oi en i y a viny' one uori e resin om ennwa emica millatlon utlhzed m evaluatmg gach of the earners com Lexan 105 is a trademark used to identify a poly Bisphenol-A carbonate PIISCS: 40 resin from General Electric; Lucite 2041 is a trademark used to identify G a methyl methacrylate resin from Du Pont; Polysulfone P1700 is a trademark used to identify a diphenylene sulfone resin from Union Poly( 4,4 -isopropylidene diphenyLalt-ethyIene car- Carbide; Polysulfone P3500 is a trademark used to identify a diphenylene b 200 sulfone resin from Union Carbide; Saran F220 is a trademark used to identify a vinylidene chlorlde-acrylonitrile copolymer from Dow Chem- Aerosol TR (a trademark) [bis-tridecyl ester of sulical, which appears to be 85% vinylidene chloride and 15% acrylonitrile.

fosuccinic acid sodium salt purchased from American Cyanamid Co.] 2 EXAMPLE 2 glgrosmepasqdwolor Index 5041513) 2 Several of the more promising resin materials of Table g g S FT t d k bt d I and several other carrier surface coatings materials are on g g mg (a [a emar 0 11 4 tried on sponge-iron particles, i.e. rough-surfaced iron C P 5 0 particles. These particles have an average diameter within oor aancmg yes the range of 80-120 mesh and are obtained from the 2% by weight of the control toner is used to evaluate d-Ioeganaes Corp. as Hoeganaes EH iron particles. The each of the'carrier vehicles. sponge iron materials are coated with an amount of resin An evaluation is made to find coated carriers which exas indicated in Table II and the following results are obhibit high net toner charge. tained. In each of these tests a toner identical to that de- The resistivities reported herein are measured using thescribed in Example 1 is used in an amount as indicated resistance test described hereinbefore. in Table H.

TABLE Ii J x Scumnung Weight percent Fine of back- Net Throw- Image line ground Resistivity toner Carrier coating Coating Toner all type rcpro. image areas (ohms) charge None (control) i "i" 7 '11 0(6 0'i' 8% 3 0 I g F g F g 1 i0 2 Vin lidene chloride 79 -ac onitri e 15 -acry 'c aci r Kyi iar; w o 0 1.0 6.0 H-M s-s. G G 0x10 Polystyrene r 0.8 5.0 M S G G 1X1(]7 6 20 Cellulose acetate butyrate 1.0 5.0 H S E G 4X10 6.70 Cellulose nitrate 0.5 6.0 M M G G 1X10 CPF 0.5 6.0 H-M S-F P E 0x10 8 48 Barex 210-. 0.5 4.0 H s-s F-G G 4x10 0 72 Saran 210 1 0.5 5.0 Ir'M S-F G E 2X10 8 11 Milvex 4000.-- 0.5 0.0 H-M' 8-8 G G 4x10 LEGEND.Throw-ofi: L= Light, M= Medium, H =Heavy. Fine line reproduction; l Poor, F Fair, G Good, E Excellent. Scum1m'ng of background image areas: G Good (little scumming) E =Excellent (almost no scumming visible); CPE is a trademark identifying a chlorinated polyethylene made by Dow Chemical Co Barex 210 is atrademark identifying an acrylonitrile-ethyl acrylate oopolymer. Saran F310 .15 a trademark identifying a vinylidene chloiide-acrylonitrile copolymer from Dow Chemical. 'lvex 4000 is a. trademark identifying a soluble polyarnide resin from General Mills;

It will be noted from Table I and Table II that the optimum composite results appear to be con istent1yobtained with the vinylidene chloride-acrylonitrile-acrylic acid coatings of this invention. The closely related Saran materials, while exhibiting some improved characteristics, appear to produce'lower net toner charge with concomitant higher toner throw-01f than the resin coatings used in the present invention.

EXAMPLE 3 To show the importance of the organic acid monomer,- the series of tests described in the following table, are run utilizing a 0.1% by weight vinylidene chloride-acrylonitrile-acrylic acid resin coating on iron particles. The iron particles are identical to those described in- Ex. 2. In each of these tests the toner is identical to that described in Ex. 1. As the results of these tests show (see Table III), by increasing the acid component of the copolymer, a higher net charge is imparted to the toner particles.=

TABLE IIL-COMPOSITION OF TERPOLYMER CARRIER- The following tests indicate that the acrylonitrile content of the terpolyrneric coating materials useful in the invention may also be varied as noted above. In each of these tests the iron particles which are coated are identical 35 TABLE V Net toner Toner charge throw-ofl Carrier coating (acouL/g.) (milligrams) Vinylidene chloride (79%)-acrylonitrile (15%)-acry1icacid (6%) terpolymer 11. 7 1. 6 Poly(acry1onitrile) 1 13. 5 1. 9 Po1y(methacrylonitrlle) 1. 3 83. Po1y(vinylidene chloride).- 2. 103. 2 Poly(acrylic acid) 3 11.7 1. 8 Poly(vinyl pyridine) 4. 0 26. 0 10 Copolymer formed from equal parts by weight of vinyl pyridine and acrylic acid 3. 5 42. 0 Copolymer of equal parts by weight of methylvinylether and maleic anhydride. (This eopolymer corresponds to compound V, Table I of Miller U.S. Pat. 3,- 547,822,issuedDec.15,1970.) 10.7 2.7 Copoly'mer of equal parts by weight of styrene and maleic anhydri de. (This copolymer corresponds to Compound IV, Table I of Miller, U.S. Pat. 3,547,822, issued Dee. 15, 1970 10. 8 4. 0

1 Poly(acrylonitrile) has not been found to be as useful a carrier coating material because the resultant coated carrier particles, when utilized together with a toner powder in a magnetic brush apparatus, exhibit toner replenishment rates which are substantially less than those exhibited by material because it is so soft that it is easily abraded. Thus, poly(acrylic acid) does not exhibit sufificient abrasion resistance to provide a practical carrier coating material. In addition, poly(acrylic acid) exlnbits poor environmental stability under high relative humidity conditions.

The invention has been described in detail with particular reference to certain preferred embodiments thereof,.

but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. In an electrographic developing composition for use in developing electrostatic charge patterns comprising a physical mixture of magnetically attractable carrier par- Weight Percent by weight percent Repro- Canier Net toner in Toner duction Vinylidene Acry lo- Acrylic resistoner developer throwof fine chloride nitrile acid tivity charge mix-., 0 lines 10 0s 1.5)(10 10.33 6 L E 15 06 5X10 .10.77' 6. L G-E 30 06 1x10 710.76 I 5 L G EXAMPLE 5 ticles and electroscopic toner particles, the improvement In this example, a series of tests are run to compare ithe terpolymeric coated carriers and a deveiapereofitain :ing the same to carriers coated 'th k oat- W1 nown resmous 5 about to about 93% by weight vinylidene chloride;

(b) from about 5 to about 3 0% by Weight of at least one iing materials which are somewhat similai'fto the terpoly mer coatings used in the present inventionrln this 'J ample Net Toner Charge and Toner Throw Oif have been; investigated. In each of the tests the carrier particles are coated with an amount of polymer equal to 0.3% by wherein said carrier particles comprise cores of magnetitcally-attractable.materialrhaving.thereona coating of a polymer comprising a copolymerized blend of (a) from member selected from the group consisting of acrylonitrile, methacrylonitrile, and an alkyl ester of an acrylic or methacrylic, acid having from l-18 carbon atoms in weight of the total weight of the coated carrier particles; alkyl group? and (c) from about 2 about by In each test, a developer composition is formed composed] of 9 5 by weight of each of the indieated polymencoated particulate carrier vehicles and 5% byweightof. anide'n-j tical control toner formulation oompris'ing pigmentedthen moplastic resin particles, i

13 N NaOH per gram of polymer based on the dry weight of said polymer.

2. The invention of claim 1 wherein said polymer is a vinylidene chloride-acrylouitrile-acrylic acid terpolymer.

3. The invention of claim 1 wherein said polymer is a terpolymer comprising a copolymerized blend of about 15% by Weight acrylonitrile, about 6% by weight acrylic acid, and about 79% by Weight vinylidene chloride.

4. The invention of claim 1 wherein the magneticallyresponsive core contains a material selected from the group consisting of iron, nickel, cobalt and alloys and mixtures thereof.

5. The invention of claim 1 wherein the average size of the carrier core particles is from about 30 to about 1200 microns.

6. An electrographic developer composition comprising a mixture of from about 1 to about 10 weight percent of electroscopic toner particles and from about 90 to about 99 weight percent of carrier particles wherein each carrier particle comprises a core of ferromagnetic material having thereon a coating of a vinylidene chloride-acrylonitrile-acrylic acid terpolymer, said terpolymer comprising a copolymerized blend of from about to about 30% by weight acrylonitrile, from about 2 to about by 25 weight acrylic acid, and from about to about 93% by weight vinylidene chloride, said terpolymer having an acid content less than 2 milliequivalents of 1N NaOH per gram of terpolymer based on the dry weight of said terpolymer.

7. The invention of claim 6 wherein the ferromagnetic material is selected from the group consisting of iron and iron alloys and wherein the average size of the carrier core particles is within the range of from about to about 300 microns.

8. The invention of claim 6 wherein said terpolymer comprises from about 0.001 to about 3 percent by weight of said carrier particles.

References Cited UNITED STATES PATENTS 3,669,885 6/ 1972 Wright 252--62.1 3,533,835 10/1970 Hagenbach et a1. 252-62.1 3,547,822 12/1970 Miller 252-621 3,526,533 9/ 1970 Jacknow et al 25262.1 2,874,063 2/1959 Greig 25262.1 2,857,290 9/1958 Bolton 252-621 FOREIGN PATENTS 1,174,571 12/ 1969 Great Britain 25262.1

NORMAN G. TORCHIN, Primary Examiner I. P. BRAMMER, Assistant Examiner US. Cl. X.R. 117-100 N 

